Cohesive elements do not converge when combined with ductile damage

[WillingToLearn]

Hello,

I have a model consisting of three components: Fibre (Isotropic), Interface (Cohesive Elements) and Matrix (Ductile Damage).

If I run the model without the ductile damage, it works fine -> Interface fails

If I run the model without the interface, it works fine (second picture) -> Matrix fails

But when I run both together, the interface starts failing and failure is also initiated in the matrix but then it does not converge: "Time increment required is less than the minimum specified".

I suspect that has something to do with the fact, that the matrix material starts failing at the cohesive interface.

At the point of non convergence, the dissipation energy spikes:

Settings:

One part with different sections assigned to it

Units: Length[µm], Time [ms], Stress [GPa]

Periodic Boundary conditions

Solver: Unsymmetric (as recommended in the manual)

Minimum time step: E-25ms

Maximum time step: 10ms

NLGeom: On

Specific dissipated energy fraction: 0.0002

Max ratio of stabilization to strain energy: 0.05

Maximum degradation (matrix&interface): 0.99


I've spend many hours trying to find a solution but was not successful. I also asked in the simulia forum, but was not able to solve the issue. Do any of you have a suggestion for me?

Kind regards

Mike

 

[FEA way]

Sometimes it helps when you adjust the solver controls, especially in the case of highly nonlinear damage and fracture mechanics problems. Do you use static step here ?

 

[WillingToLearn]

Thank you for answering so quickly. The pictures above show a static step, but I also tried implicit dynamic and it did not change anything.

Which solver controls would you recommend to change? I have basically no experience with this.

 

[FEA way]

You can try this:
- turn on discontinuous analysis
- increase the max number of attempts to 20

This is recommended for XFEM analyses but there’s a chance that it will help here as well.

Apart from that, enable viscous regularization in element type settings.